Many lighting systems for illuminating an environment such as a room, employ one or more light sensors to sense an amount of light in the environment and to adapt the emitted illumination in dependence on the sensed level of light, e.g. to adapt the emitted illumination in dependence on the amount of daylight in the environment. An existing problem in such lighting systems designed is how to perform calibration of light sensors easily and accurately for proper control operation.
A light sensor is typically mounted on the ceiling, facing-down so as to measure the light reflected back to it from the surface or surfaces below. Thus for a given illumination at the horizontal workspace plane, the amount of light the light sensor measures may differ depending on the reflectance of the surface(s) in its field of view. The objective in most lighting control applications is to maintain a specified illumination level at the height of the horizontal workspace plane, for example, over the top surface of a desk. However the control of the illumination is based on the sensor measurements taken by the sensor on the ceiling, so as to achieve a reference set-point defined for the light sensor reading. As such, a relation needs to be established between the sensed light level at the sensor and the actual light level at workspace below it, which is done via calibration.
Existing calibration methods rely on manual commissioning wherein a commissioning agent turns on the luminaires at a specific, known dimming level, e.g. fully, and measures the illuminance using a light meter placed at one or more positions in the workspace plane. The light sensor measurements are then suitably scaled based on the workspace light meter measurements, in order to determine controller set-points such that a desired illuminance at workspace plane is met.